兰州大学机构库 >物理科学与技术学院
重夸克偶素的强跃迁和重味介子之间的相互作用
Alternative TitleThe strong transitions of heavy quarkonia and interactions between heavy mesons
王波
Thesis Advisor刘翔
2018-03-31
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword有效场论 重夸克偶素 重介子 强跃迁 相互作用 分子态
Abstract

近年来,随着对撞机实验能量及精度的不断提升,已有越来越多的新粒子被人们发现。这包括目前了解仍不透彻的$X, Y, Z$等一系列新强子态,还包括大量近阈的普通强子。这些近阈普通强子的衰变性质与远离阈值的粒子有很大的差别。例如,对于在阈值以上的高激发态重夸克偶素(粲偶素和底偶素)而言,它们跃迁衰变的分支比和$\pi\pi$不变质量谱就很反常。虽然QCD多极展开在描述低激发态重夸克偶素的强跃迁时非常成功,但到高激发态,QCD多极展开便显得无能为力。在传统理论框架下无法解释的新现象促使我们运用新的机制来理解这些异常的实验信息。

在本论文中,我们先研究了$D$波粲偶素$X(3823)\to J/\psi\pi^+\pi^-$的跃迁。我们发现理论预言的$\pi^+\pi^-$的不变质量谱在低能部分与实验数据不符,考虑到$X(3823)$的质量靠近$D\bar{D}^\ast$的阈值,所以在该过程中我们又加入了耦合道效应。我们的计算结果表明耦合道效应的贡献与QCD多极展开的贡献在同一量级,且考虑了耦合道效应后的$\pi^+\pi^-$的不变质量谱能更好地描述实验信息。

紧接着,我们又研究了高激发态底偶素$\Upsilon(5S)\to\Upsilon(1^3D_J)\eta$的跃迁。我们先用QCD多极展开对该过程的跃迁分支比做了计算,发现$\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_1)\eta]\simeq4.7\times10^{-6}$,$\mathcal{B}[\Upsilon(5S)$\\$\to\Upsilon(1^3D_2)\eta]\simeq8.4\times10^{-6}$,$\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_3)\eta]=0$。我们进一步计算了强子圈的贡献后发现$\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_1)\eta]\simeq(0.5\sim5.1)\times10^{-3}$,$\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_2)\eta]\simeq(0.7\sim7.5)\times10^{-3}$,$\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_3)\eta]\simeq(0.9\sim9.6)\times10^{-4}$。也就是说强子圈的贡献在该过程中起主导作用,2018年的Belle实验证实了我们的预言。

此外,我们也用手征有效场论的方法将$\bar{B}\bar{B}$,$\bar{B}\bar{B}^\ast$和$\bar{B}^\ast\bar{B}^\ast$系统的有效势计算到了单圈,发现$I(J^P)=0(1^+)$的$\bar{B}\bar{B}^\ast$和$\bar{B}^\ast\bar{B}^\ast$系统的有效势是吸引的。解薛定谔方程后得到这两个道的束缚能分别为$\Delta E_{\bar{B}\bar{B}^\ast}=-18_{-31.5}^{+17.6}$ MeV和$\Delta E_{\bar{B}^\ast\bar{B}^\ast}=-99_{-87.9}^{+73.2}$ MeV。该研究不仅可以为未来实验上寻找含有双底夸克的奇特分子态提供有用的信息,而且对以后格点QCD计算$\bar{B}^{(\ast)}\bar{B}^{(\ast)}$系统的有效势以及手征外推都很有帮助。

Other Abstract

In recent years, more and more new particles have been observed with the improvement of colliding energy and measuring precision at experiment. These include the poorly understood exotic states, like $X, Y, Z$, and a number of ordinary hadronic states but with masses close to the threshold. The decay patterns of these new states near threshold are very different with the low-lying ones. For example, the hadronic transitions of largely excited heavy quarkonium are more complicated, and thus the branching fractions and invariant mass spectra are anomalous. Although the QCD multipole expansion is very successful in describing the hadronic transitions of low-lying excited heavy quarkonium, but it turns to break down for above-threshold states. The uncomprehensible phenomena in traditional framework prompt us to use new mechanism to interpret the anomalous experimental data.

In this work, we firstly studied the dipion transition of $D$-wave charmonium $X(3823)$, i.e., $X(3823)\to J/\psi\pi^+\pi^-$. We noticed the $\pi^+\pi^-$ mass spectrum predicted by QCD multipole expansion is inconsistent with the experimental data at low energy region. For the mass of $X(3823)$ is very close to $D\bar{D}^\ast$ threshold, we considered the coupled-channel effect for this process. Our results show that the contribution from the coupled channel is in the same order of magnitude with the direct channel. Furthermore, with the coupled-channel effect being involved, the $\pi^+\pi^-$ mass spectrum can be reproduced to fit the experimental data better.

Next, we focused on the $\eta$ transition of $\Upsilon(5S)$ to $D$-wave bottomonium $\Upsilon(1^3D_J)$, viz, $\Upsilon(5S)\to\Upsilon(1^3D_J)\eta$. We firstly evaluated the branching fractions via QCD multipole expansion, the results are $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_1)\eta]\simeq4.7\times10^{-6}$, $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_2)\eta]\simeq8.4\times10^{-6}$, $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_3)\eta]=0$. But the hadronic loop mechanism predicts $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_1)\eta]\simeq(0.5\sim5.1)\times10^{-3}$, $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_2)\eta]\simeq(0.7\sim7.5)\times10^{-3}$, $\mathcal{B}[\Upsilon(5S)\to\Upsilon(1^3D_3)\eta]\simeq(0.9\sim9.6)\times10^{-4}$. This indicates that the contribution from hadronic loop mechanism is dominant, and the recent Belle experiment has confirmed our predictions.

In addition, we studied the effective potentials of $\bar{B}\bar{B}$, $\bar{B}\bar{B}^\ast$, and $\bar{B}^\ast\bar{B}^\ast$ systems with chiral effective field theory up to one-loop level, and found the potentials in $0(1^+)$ $\bar{B}\bar{B}^\ast$ and $\bar{B}^\ast\bar{B}^\ast$ systems are attractive. After solving schr\"odinger equation, we obtained the binding energies are $\Delta E_{\bar{B}\bar{B}^\ast}=-18_{-31.5}^{+17.6}$ MeV and $\Delta E_{\bar{B}^\ast\bar{B}^\ast}=-99_{-87.9}^{+73.2}$ MeV for $\bar{B}\bar{B}^\ast$ and $\bar{B}^\ast\bar{B}^\ast$ systems, respectively. The study on $\bar{B}^{(\ast)}\bar{B}^{(\ast)}$ interactions not only provides some useful information to explore exotic double-bottom molecular states for future experiments, but also is helpful for the extrapolations of Lattice QCD simulations.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229007
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
王波. 重夸克偶素的强跃迁和重味介子之间的相互作用[D]. 兰州. 兰州大学,2018.
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